In many industries certain processes require pressure measurements over a wide range from about 1000 Torr to less than 10−9 Torr. For example, some semiconductor and electronic device manufacturing processes require accurate pressure measurements from ultrahigh vacuum to atmospheric pressures. To achieve the wide-range pressure measurement requirements of industry, there has been a recent movement to combine vacuum gauges having different pressure measurement ranges into a single product. These products typically include at least two different physical means for measuring pressure in a given environment.
In some applications it is necessary not only to measure pressures over a wide range, but also to measure absolute and differential pressure simultaneously. For example, in certain applications, the pressure inside a chamber must be slightly greater than the pressure outside the chamber. Otherwise, if the pressure inside the chamber were less than the pressure outside the chamber and the chamber door were opened, then contaminants could enter the chamber. Also, if the pressure inside a chamber were much greater than the pressure outside the chamber and the chamber door were opened, then turbulence could damage the product being processed. In order to achieve the slight pressure differential between the inside and the outside of the chamber, it is necessary to obtain accurate differential pressure measurements.